With continuous evolution of wireless cellular networks, orthogonal multiple access technologies, such as a Code Division Multiple Access (“CDMA” for short) technology and an Orthogonal Frequency Division Multiple Access (“OFDMA” for short) technology, widely applied in third generation (3rd-Generation, “3G” for short) and fourth generation (4th-Generation, “4G” for short) mobile communications systems gradually cannot meet requirements of people for a larger cellular network capacity, for example, for massive access and continuous spectral efficiency improvements. Moreover, the industrial field and academic field gradually pay more attention to research and application of a non-orthogonal multiple access technology, and people expect that a capacity of a future wireless cellular network, such as a fifth generation (5th-Generation, “5G” for short) mobile communications system, can be effectively improved by using the non-orthogonal multiple access technology.
A sparse code multiple access (“SCMA” for short) technology is a typical non-orthogonal multiple access technology. Certainly, the SCMA technology may have another name in the field of communications. According to the technology, M (M is an integer not less than 1) data streams from one or more users are superimposed on N (N is an integer not less than 1) subcarriers for sending. Each piece of data of each data stream is extended on the N subcarriers by means of sparse spread spectrum. When M is greater than N, the technology may effectively improve a network capacity, including a quantity of users that can access a system, spectral efficiency, and the like. Therefore, as an important non-orthogonal access technology, the SCMA technology attracts more attention, and becomes an important candidate access technology during evolution of the future wireless cellular network.
In a non-orthogonal multiple access system such as an SCMA system, when a terminal device receives a downlink data stream that is sent by a network device by using a non-orthogonal multiple access technology, the terminal device needs to learn a codebook used for the downlink data stream. However, selection and allocation of the codebook are generally completed by the network device, and the terminal device does not participate in such a process directly. Therefore, how the network device notifies the terminal device of an allocated codebook after allocating the codebook for a data stream to be received by the terminal device is a technical problem that urgently needs to be resolved.